1. Technical Field
The present invention relates to a phosphor composition and a white light emitting device using the phosphor composition. More particularly, the present invention relates to a phosphor composition and a white light emitting device using the phosphor composition to provide better light type, thermal stability and no power saturation.
2. Description of Related Art
With rising awareness of carbon reduction and sustainable development, advanced countries around the world are gradually phasing out traditional high energy-consuming lighting with white light emitting diodes (LEDs) as replacement. White LEDs advantageously have small size and thus can be adjusted depending on the application. Given the fast response time, white LEDs are suitable for high frequency operation. White LEDs have low power consumption, which is about ⅛ to 1/10 of that of traditional bulbs and ½ of that of fluorescent bulbs. Moreover, white LEDs have relatively long life of up to 100,000 hours. Accordingly, white LEDs can be a solution to the problem of high energy consumption by incandescent bulbs. Thus, white LEDs can be used as a new lighting and display light source, and promote the concepts of energy saving and environmental protection. They are considered as a “green” light source.
The technology related to white LEDs was introduced in the 1990s. Basically, cerium-doped yttrium aluminum garnet phosphor (Ce-doped YAG phosphor) is excited by blue LED to produce yellow light. The yellow light is mixed with remaining blue light emitted by the blue LED to produce white light. However, yttrium aluminum garnet phosphor, as used in white light technology, tends to have the problem of power saturation; namely, any increase in brightness is limited after the brightness of the yellow light produced by excitation of yttrium aluminum garnet phosphor has reached a certain level.
Since the year 2000, white LEDs based on yellow silicate phosphor has become an alternative white light technology. Nevertheless, although silicate phosphor does not have power saturation problem, it tends to suffer the problem of thermal stability. That is, after being exposed to an environment of intense heat for a long time, the brightness of the yellow light produced by silicate phosphor tends to decay gradually. This will result in reduction of brightness of white light and color temperature shift, in addition to the susceptibility to damp and breakdown. Therefore, it is imperative to develop a new phosphor composition that avoids the aforementioned problems.